This patent application claims priority based on a Japanese patent application No. 2000-206063 filed on Jul. 7, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a power-source system, a power supplying method and an image capturing apparatus. More particularly, the present invention relates to a power-source system that allows a power source to supply an electric power to a load, a power supplying method that can be used in the power-source system, and an image capturing apparatus that can use the power-source system.
2. Description of the Related Art
A power-source system that outputs a predetermined voltage to a device, obtained by raising or reducing a voltage supplied from a power source. The predetermined voltage is supplied as electric power to the device such as a camera.
FIGS. 1A and 1B show temporal changes of a battery voltage in a conventional power-source system. FIG. 1A shows a discharge curve of a battery. Generally, the voltage of the battery gradually falls because of the discharge. In a case where the voltage of the battery falls in accordance with the discharge curve as shown in FIG. 1A, the voltage falls below a level of a consumption limit at time t0. The consumption-limit level is set such that a decision that sufficient power cannot be supplied to the device should be made. Thus, at the time t0, it is determined that the battery cannot be used, thereby stopping the use of the battery.
FIG. 1B shows the voltage of the battery used in an actual power-source system. With the consumption of electric energy of the battery, the voltage of the battery gradually falls in accordance with the discharge curve of the battery. In a case where the device performs an operation that momentarily requires a large current, however, the voltage of the battery falls suddenly. Such a phenomenon occurs, for example, when a motor is driven in a camera.
In the above case, since the battery voltage falls below the consumption-limit level at time t1 because of the operation requiring the large current, as shown in FIG. 1B, it is determined at the time t1 that the energy of the battery has been consumed to reach such a level that the battery can no longer be used and therefore the use of the battery should be stopped at the time t1. However, the sudden fall of the voltage at the time t1 is caused by the operation by the device that momentarily requires the large current and therefore the voltage of the battery actually is still at a level at which the battery can be used. In other words, although the battery can still be used, the use of the battery is stopped. Therefore, the electric energy of the battery cannot be used efficiently. Moreover, the use of the battery is stopped at the time t1 although the battery can actually be used until the time t0. Therefore, a time period in which the device can use the battery is shortened.
Therefore, it is an object of the present invention to provide a power-source system, a power supplying method and an image capturing apparatus that overcome the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a power-source system includes: a power source; a voltage monitoring unit operable to monitor a voltage of the power source to detect that the voltage falls below a consumption-limit level below which the use of the power source is to be limited; a consumption limiting unit operable to limit the use of the power source when the voltage falls below the consumption-limit level; and a limit prohibiting unit operable to prohibit the consumption limiting unit from limiting the use of the power source when the voltage of the power source falls below the consumption-limit level because of a momentary voltage fall different from a voltage fall corresponding to a discharge curve of the power source.
The limit prohibiting unit may include a nullifying unit operable to prevent a result of the detection by the voltage monitoring unit from being sent to the consumption limiting unit prior to the momentary voltage fall. Alternatively, the limit prohibiting unit may include a disabling unit operable to disable the voltage monitoring unit prior to the momentary voltage fall. Alternatively, the limit prohibiting unit may include a nullifying unit operable to prevent a result of the detection by the voltage monitoring unit from being sent to the consumption limiting unit when the momentary voltage fall is detected.
According to the second aspect of the present invention, a power supplying method for supplying power to a load from a power source, includes: limiting supply of the power when a voltage of the power source falls below a predetermined level; and prohibiting the supply of the power from being limited in a case where the load requires a larger current than a current required normally, even if the voltage of the power source momentarily falls below the predetermined level.
According to the third aspect of the present invention, an image capturing apparatus for capturing an image, includes at least one component performing a predetermined operation and a power-source system for supplying a power to the one component, wherein the power-source system includes: a power source; a voltage monitoring unit operable to output an abnormal signal when the voltage falls below a consumption-limit level below which the use of the power source is to be limited; a consumption limiting unit operable to limit the use of the power source when receiving the abnormal signal from the voltage monitoring unit; and a limit prohibiting unit operable to prohibit the abnormal signal from being received by the consumption limiting unit in a case where the voltage of the power source falls below the consumption-limit level because of a momentary voltage fall caused by an occurrence of a heavy-load state requiring a larger current than a current required in a normal-load state.
The heavy-load state causing the momentary voltage fall may be a state caused by an operation for driving the at least one component by using a motor.
The image capturing apparatus may further include a limit-prohibition requesting unit operable to send the limit prohibiting unit a request of prohibiting the abnormal signal prior to the occurrence of the heavy-load state.
The limit prohibiting unit may allow the abnormal signal to be sent to the consumption limiting unit in the absence of the request of prohibiting the abnormal signal.
The image capturing apparatus may further include a prohibition-time setting unit operable to set a prohibition time in accordance with a type of the heavy-load state, the prohibition time being a time period during which limiting the use of the battery is to be prohibited.
According to the fourth aspect of the present invention, a power-source system includes: a power source; a voltage monitoring unit operable to detect that a voltage of the power source falls below a consumption-limit level below which the use of the power source is to be prohibited; a consumption limiting unit operable to limit the use of the power source when the voltage falls below the consumption-limit level; and a limit prohibiting unit operable to prohibit the consumption limiting unit from limiting the use of the power source when the voltage of the power source falls below the consumption-limit level because of a momentary voltage fall different from a voltage fall corresponding to a discharge curve of the power source, wherein the voltage monitoring unit includes a comparator operable to compare the voltage of the power source to the consumption-limit level, the limit prohibiting unit includes a disabling unit operable to disable the comparator when the momentary voltage fall is expected to occur, the disabling unit lowering the consumption-limit level to such a level that the comparator detects no fall below the consumption-limit level.
According to the fifth aspect of the present invention, an image capturing apparatus includes; at least one component operable to perform one of a plurality of operations necessary for capturing an image; a power-source system for supplying power to the at least one component; and a controller operable to control the at least one component and the power-source system, wherein the power-source system includes: a power source for supplying the power; a voltage monitoring unit operable to monitor a voltage of the power source to detect that the voltage of the power source falls below a predetermined level; a consumption limiting unit operable to stop the supply of the power from the power source when the voltage of the power source falls below the predetermined level; and a limit prohibiting unit operable to prohibit stopping the supply of the power by the consumption limiting unit for a predetermined time period in accordance with a request from the controller, the controller sends the request to the limit prohibiting unit when an operation by the at least one component is an operation expected to cause a momentary voltage fall.
The length of the predetermined time period maybe determined in accordance with a type of the operation expected to cause the momentary voltage fall.
The image capturing apparatus may further include a memory operable to store the operation expected to cause the momentary voltage fall, wherein the controller determines whether or not the operation by the at least one component is the operation stored in the memory.
The memory may store an operation for driving the at least one component by using a motor as the operation expected to cause the momentary voltage fall.
The controller may send the limit prohibiting unit the request prior to the operation stored in the memory.
The limit prohibiting unit may prohibit stopping the supply of the power by making a result of the detection by the voltage monitoring unit ineffective. Alternatively, the limit prohibiting unit may prohibit stopping the supply of the power by lowering the predetermined level to such a level that no momentary voltage fall below the predetermined level expected to be caused by an operation by the at least one component is detected.
This summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the above described features. The above and other features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings.